The present application is based on Japanese Patent Application No. 2001-182544, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a light-emitting device and particularly to a device using a light-emitting element which emits light in a relatively short wavelength range. The light-emitting device according to the invention can be used as a light source for illumination or as a light source for various kinds of display devices.
2. Description of the Related Art
A device configured as shown in FIG. 5 is known as a light-emitting device using a light-emitting element. FIG. 5 typically shows an SMD (Surface Mounted Device) type LED 100. The LED 100 is produced as follows. A light-emitting element 110 is disposed into a cup-like portion 150 formed by a combination of a substrate 120 and a reflector (casing) 130. The cup-like portion 150 is filled with a sealing member 140 (light-transmissive resin). The reflector 130 is made of a polymer resin containing a white filler such as titanium oxide. On the other hand, the sealing member 140 is generally made of an epoxy resin.
Under the existing circumstances, the light-emitting element used in the SMD type LED exhibits an emission peak wavelength in a relatively long wavelength range such as a red region. The epoxy resin used as the sealing member is relatively durable against light emitted from the light-emitting element. Accordingly, the color in the epoxy resin may be more or less changed in long-term use but the degree of the change of the color is small.
Incidentally, a short wavelength light-emitting element exhibiting an emission peak wavelength in an ultraviolet region has been being developed in the expectation that the element will be applied to an SMD type LED. Therefore, the present inventors have tried to form an SMD type LED by use of a short wavelength light-emitting element. As a result, it has been found that the deterioration (color change) of the sealing member is too fast to withstand practical use in terms of durability when an epoxy resin is used as the sealing member in the related-art manner.
On the other hand, in order to secure the stability and reliability of the light-emitting device, it is necessary to form the sealing member in a state in which no gap is generated between the sealing member and a base member (including a reflector) on which the light-emitting element is mounted. That is, sufficient adhesion (close contact) is required between the sealing member and the base member.
The inventors have examined the material of the sealing member and the base member in consideration of the problem. As a result, it has been found that silicone as the material of the sealing member exhibits very high durability against light in a short wavelength region. From the point of view of adhesion between the sealing member and the base member, the inventors also have made examination. According to the examination result, it has been found that good adhesion is obtained between the sealing member and the base member when a polyamide-based resin is used as the base member in the case where silicone is used as the sealing member. The invention is based on the findings and is configured as follows.
A light-emitting device including a semiconductor light-emitting element, a base member provided so that the semiconductor light-emitting element is mounted on the base member, and a sealing member provided so that the semiconductor light-emitting element is coated with the sealing member, wherein:
at least one portion of the base member is made of a polyamide-based resin; and
at least one portion of the sealing member is made of silicone.
According to this configuration, sufficient adhesion (close contact) is obtained between the sealing member and the base member, so that the sealing member can be formed in a state in which no gap is generated between the sealing member and the base member. Accordingly, both stability and reliability of the light-emitting device are improved. In addition, because silicone exhibiting high durability against light in a short wavelength region is used as the material of the sealing member, the deterioration of the sealing member is suppressed to improve durability of the light-emitting device particularly when a short wavelength semiconductor light-emitting element is used.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.